Japanese Patent Application No. 15491/55:1980 (TOKKO) discloses a process wherein a three-neck flask equipped with a stirring apparatus, a nitrogen gas introduction orifice, and a distilling-out orifice was charged with 25.4 parts of a polycarbonate (.eta.sp/C=0.98) which was obtained by using bisphenyl A as the dihydroxy component, 13.0 parts of 2,6-naphthalenedicarboxylic acid (60 mole % relative to the bisphenol A component in the polycarbonate), and 0.005 parts of titanium tetrabutoxide. After the flask was purged with nitrogen, reaction was conducted at 300.degree. C. under normal pressure for 30 minutes, then further under reduced pressure of about 20 mmHg for 1 hour, whereupon carbon dioxide gas evolved and the reaction mixture became transparent.
Next, 14.1 parts of diphenyl carbonate were added and reaction was conducted at 300.degree. C. under normal pressure for 30 minutes; then the system was gradually depressurized and, 20 minutes later, reaction was conducted under reduced pressure of 0.5 mmHg for 1 hour. The .eta.sp/C of the polymer was 0.712, its melting point was 225.about.245.degree. C., and its thermal deformation commencement temperature was 188.degree. C.
The process described in Japanese Patent Application No. 15491/55:1980 (TOKKO) consists essentially of two steps: (1) heating the polycarbonate with 2,6-naphthalenedicarboxylic acid to evolve carbon dioxide and obtain a hydroxyl-terminated prepolymer; and (2) reaction of diphenyl carbonate with the hydroxyl-terminated prepolymer to liberate phenol and obtain a high molecular weight polyester or poly(ester-carbonate). It should be noted that this process always involves the second-step reaction with diphenyl carbonate.
It should be further noted that the Japanese Patent Application does not disclose the fact that the hydroxy-terminated prepolymer from the first step of their process may be heated under vacuum to eliminate bisphenol A and give a high molecular weight polymer without the addition of diphenyl carbonate. This is the difference between the Japanese process and our new process.